[asterisk-users] hum noise

[Wilton Helm]

Yes, you make a good point.  Electromagnetic fields are another source of ingress, whether from a nearby cell phone or by being located a mile away from a 50 KW AM radio transmitter (etc.).

>one does wonder why there's such inadequate shielding 

As a ham radio operator, I can say that has been a question raised about consumer electronics in general for many decades, particularly since the advent of solid state devices with their low voltage diode detecting capability.  The  answer, unfortunately, is simple--economics.  If only 1 out of 1000 devices is exposed to a situation that results in interference, the manufacture is loathe to spend even a nickel to protect against it--especially if the volume is large.  Five cents on 1,000,000 products is $50,000.  Depending on the strength of the interfering signal, it can take a lot more than five cents to protect it.  Cell phones aren't very high power,  The 50 KW transmitter--well that's another story.

Wilton
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